On my 420SEL. I replaced the stock alt with a AL129X rebuilt from AutoZone...first replacement unit had a bad bearing.. after a week I replaced it with a replacement unit..

Now a week later..the car is dead. Battery read 7V across it.

I throw on the charger..a few hours later I get the car started.

I measured battery voltage at 11.9V..clearly no alt.

I measure from the alt's power cable at the distribution block to ground...26V!

I performed continuity tests between the battery's positive terminal and the upper half of the two post distribution point.. got continuity there but nothing between the battery and the lower point... WEIRD.